Field of the Invention
One or more embodiments of the present invention relate to a negative active material and a lithium battery including the negative active material.
Description of the Related Art
Lithium secondary batteries used in portable electronic devices for information communication, such as PDAs, mobile phones, notebook computers, and the like, electric bicycles, and electric vehicles exhibit a discharge voltage that is twice or more than that of general batteries, and thus may have a high energy density.
Lithium secondary batteries include a positive electrode and a negative electrode that include an active material that allows intercalation and deintercalation of lithium ions, and an organic electrolyte or a polymer electrolyte interposed therebetween. Such lithium secondary batteries generate electric energy according to an oxidation/reduction reaction occurring when lithium ions are intercalated/deintercalated in the positive and negative electrodes.
Positive active materials of lithium secondary batteries may be oxides of lithium and a transition metal that allow intercalation Of lithium ions, such as a lithium cobalt oxide (LiCoO2), a lithium nickel oxide (LiNiO2), and a lithium nickel cobalt manganese oxide (e.g., Li[NiCoMn]O2, Li[Ni1-x-yCoxMy]O2).
Research into negative active materials that allow intercalation and deintercalation of lithium ions, such as various types of carbonaceous materials including artificial and natural graphite and hard carbon and non-carbonaceous materials such as Si, has been conducted.
Such non-carbonaceous materials exhibit a very high capacity density at least ten times that of graphite. However, due to volumetric expansion and contraction of a non-carbonaceous material during charging and discharging of a lithium battery, the lithium battery may have a low capacity retention ratio, a low charge/discharge efficiency, and a decreased lifetime. Therefore, there is a need to develop a high-performance negative active material with enhanced capacity and cycle lifetime characteristics.